The invention relates to an arrangement for measuring the conductivity distribution in liquids or multi-phase media with any direction of flow, especially for use in chemical engineering and power plant technology. The electrical conductivity is primarily a measure of other physical or chemical properties (such as the volumetric proportion of gas, the concentration, the type of material, etc.) of the liquid or as an indicator of the phase distribution over the measurement cross section of a multi-phase media.
Measurement of electrical conductivity is used increasingly for detenniniz the properties of liquids and multiphase mixtures, such as the proportion by volume of gas. For this purpose, the medium to be measured is energized by direct-current as well as by alternating-current voltage. The evaluation being made by defining the strictly ohmic or complex resistance. Preferably, for this purpose, wire-shaped or planiform electrodes, which are disposed parallel or concentrically to one another, are put into the medium to be measured in laboratory equipment, as well as for large-scale, initial applications. The conductivity is then measured locally, for example, with needle probes (German patent 3,201,799), or integrally between planiform electrodes (German patent 4,041,160). These methods are less suitable for determining the distribution of the local electrical conductivity over a cross section.
Frequently, therefore, tomographic methods of measuring are used for determining the property distribution of liquids or multi-phase systems over a certain cross section. Aside from the use of light radiation or particle radiation with interferometric or hagographic meffiods of evaluation, particularly the use of electrical tomographic methods, with inclusion of electrical conductivity measurements as well as of capacitive measurements, has proven its value. Aside from contactless methods with electrodes at the edge of the flow channel, methods, for which the electrodes are disposed in grid fashion transversely to the direction of flow of the medium (so-called wire mesh sensors), have become established.
In the case of a method developed at the University of Hannover (M. Boddem, N. Reinecke, D. Mewes: "Measurement of two dimensional phase distributions using a wire-mesh sensor", Proc. ECAPT, Oporto, Portugal, 1994 pp. 155-162), parallel wires are disposed in the cross section to be measured in three planes perpendicular to the direction of flow of the mediura and the conductivity between two parallel adjacent wires of a plane is always measured sequentially. The wires of adjacent planes are at an angle of 60.degree. to one another. After all measurements between two parallel adjacent wires of all three planes have been carried out, the projections of the conductivity distribution in the three directions specified by the orientation of tem wire grid are known. From these, the conductivity distribution is determined by means of an extensive tomographic reconstruction algoritbm The additional mathematical calculation of the results of the measurements greatly limits the number of wires that can be handled in practice and the attainable frequency for determining conductivity distributions over a particular cross section.